As a transition rule must have a activated trigger, and the default flow is to change the engagement program stream, I think a lead will be in one stream at a time. If you want to see that the lead in stream 3 could move back to stream 2, just add a trigger in Stream 3 and check the flow - if you can see the "Change engagement program stream" to "Stream 2", you'll be able to do this. Or you can do it mannualy, with the link you shared recently

As a transition rule must have a activated trigger, and the default flow is to change the engagement program stream, I think a lead will be in one stream at a time. If you want to see that the lead in stream 3 could move back to stream 2, just add a trigger in Stream 3 and check the flow - if you can see the "Change engagement program stream" to "Stream 2", you'll be able to do this. Or you can do it mannualy, with the link you shared recently

You can move leads back and forth between streams with a smart campaign, or you can move them to any stream, from any stream, by using the transition rules. The thing to remember is that transition rules always pull leads into a stream, so you'll need to base them on actions after which you would want your lead moved to a specific stream.

Thanks for the information. If a lead starts in Stream 1 and receives email #1 and #2, then moves to Stream 2 and starts receiving emails, if they move back to Stream 1 they will pick up with email #3 correct?

If the content in Stream 1 has not changed, then yes. A lead will always receive the next piece of content in line that they've never received before. This means content is prioritized from the top down, and that leads will not be sent any content they've received before from any source in your Marketo instance.

Another question for you, John! If I clone a Stream and add contacts that did not open any of the emails from the original stream would they be able to receive the emails in the cloned stream? I'm thinking that since they are the same emails that they would not receive it again.